Redundant systems provide multiple components for controlling a particular mechanism so that in the event that one component fails, the redundant component can still be used to control the mechanism. Redundant systems are commonly used in aircraft in which it is highly desirable to have redundancy for safety purposes.
For example, a redundant system can be utilized to control a valve within a fluid system of an aircraft. The system may include two wiring paths from the cockpit to a motor actuator used for controlling the valve. The motor actuator also may include redundant components, such as two motor controllers for commanding two motors independently of one another each powered by separate power supply sources. In the event that any component of the redundant system experiences a failure, the corresponding redundant component can be used to control the valve in accordance with the commands from the cockpit.
Under normal operating conditions, both motor controllers receive the same input commands. In some circumstances, however, it is possible for the system to be damaged such that the motor controllers receive conflicting commands or contradictory (e.g., one motor controller commanded to close the valve and the other motor controller commanded to open the valve). The receipt of contradictory commands can damage the motors and/or cause the motors to oppose each other and stall.
Depending on the relative strengths of the motors, the stronger motor may eventually overtake the weaker motor to control the valve. Predicting which motor will eventually overcome the other, however, is very difficult due to a number of factors, including for example, manufacturing tolerances and variations in wear of the motor components. It is therefore almost impossible to determine whether the valve will be commanded according to the command sent from the cockpit or according to the command that resulted from the electrical fault.